The invention relates to a lithography system comprising a light source producing a light beam directed to a mask located in a mask level and an optical demagnifier for demagnifying and focusing the beam.
Such a system is for example known from the article xe2x80x9cOptics for Wafer Steppers: The Key to the Semiconductor Industryxe2x80x9d published in xe2x80x9cInnovation 1, Carl Zeiss, 1996, pages 32 and 33.
In said article a wafer stepper is described using high-quality projection lenses to project a 4xc3x97 demagnified image of a device pattern on a mask (the reticle) in a step and repeat fashion onto a silicon wafer. Starting as machines for 1.5 xcexcm resolution in the late seventies a 4xc3x97 Deep UV steppers with 0.25 xcexcm resolution are now offered by several manufacturers. By decreasing the wavelength to 193 nm, it is expected that the 0.18 generation and probably also the 0.13 generation microcircuits could be written with the known technology.
Furthermore, in GB-A-2.164.787 and GB-A-2.260.666 a lithographic system is described, comprising a light source, a mask, a demagnifying lens and a photocathode, onto which a demagnified image of the mask is focused. The photocathode converts the light beam into a further beam of particles, in particular an electron beam. This electron beam is focused onto the object to be lithographed.
The invention has the object to provide a lithography system of the abovementioned kind, by which a resolution of less than 0.1 xcexcm could be obtained.
According to the invention, the abovementioned object is achieved in that the light beam is focused on a converter element for converting said beam in a beam having a smaller wavelength than UV light. Preferable the converter element converts the light beam in a beam of particles. However, the inventor has found that a resolution of less than 0.1 xcexcm could not be obtained, if the mask is imaged as a whole on the object to be lithographed such as in prior art systems. Only by illuminating the mask with a light beamlet which has at the mask level a transversal size smaller than the desired resolution at the object level multiplied by the demagnifying factor and scanning pixel by pixel the mask and consequently the object to be lithographed, the inventor has obtained a resolution of less than 0.1 xcexcm. It appeared that the reason of said success was the scanning operation. The image of the mask is as it were divided in pixels.
Preferably, the light source produces a plurality of light beamlets and a converter plate is provided with a plurality of converter elements, wherein the light source and converter plate are arranged such that each light beamlet is focused on one converter element. Each beamlet coming from the converter element is apertured or, alternatively, demagnified to sharpen up the pixels to less than 0.1 xcexcm.
It is notified, that from the European Patent Application EP-0605964 A3 a converter plate in form of a patterned photocathode is known per se. The photocathode lays the role of the mask according to which a wafer is lithographed. However, this technique has serious mask problems because it is a 1:1 mask and this technique is very sensitive to contamination of the photocathode. This technique is also disclosed in the European Patent Application EP-0321147 A2, the Japanese Abstract 55-87432 (A) Application nr. 53-163151 and the article xe2x80x9cA 1:1 Electron Stepperxe2x80x9d by R. Ward et al, published in 8257B Journal of Vacuum Science and Technology B, 4 (1986) January-February, No. 1, Second Series, New York.
Most other forms of high throughput electron beam lithography (shaped beam, Gaussian beam, cell projection, mask projection) are ultimately limited by stochastic Coulomb interactions between individual electrons in the beam.
From xe2x80x9cIBM Technical Disclosure Bulletinxe2x80x9d, vol. 36, No. 08, August 1993, page 379 a high throughput high resolution electron beam lithography system is known per se. This system uses the technique of multi-micro-column lithography, in which individual electron beams are focused on a wafer. However, the question of how to control such a large number of mini columns has not yet been answered.